The disclosure relates to a display window or element for viewing. More particularly, the disclosure relates to a glass display element having anti-glare properties.
The reflection of ambient light, commonly referred to as “glare,” poses a problem for displays in consumer electronic devices. In such applications, glare reduces the apparent contrast and readability of the display.
Anti-glare (AG) treatments in the form of rough surfaces typically in contact with air, by themselves or in combination with anti-reflective (AR) treatments in the form of coatings with reduced reflectivity, are common on displays having a plastic cover. As the use of strong, damage resistant glasses has become more widespread in such devices, however, the inclusion of AG and/or AR treatments becomes more problematic. It is more difficult to provide a glass surface with the degree of roughness needed to achieve AG properties, and anti-reflective coatings or films alone may not adequately reduce glare. One reason is that reflection in a glass cover device is not only produced by the exterior surfaces of the cover glass, but also by other interfaces within the display “stack,” such as surfaces of liquid crystal layers, transparent conductors, polarizers, color filters, etc.
Removing all of the internal reflections, which can create a total (i.e., diffuse and specular) reflectance of 4-15%, may be difficult. While multiple layers are present in a display, working only with the front surface of the cover glass and reducing its reflectance from, for example, 4% to below 1% creates only a partial benefit to the user. AG can be combined with AR on the front surface, for example by etching a certain surface roughness pattern into the glass and uniformly coating it with a single or multiple AR layers by magnetron sputtering. While such treatment works well in reflection, it will generally not perform as well for transmitted light reflected by interfaces below, unless the AG scattering is so great that it also degrades the visibility of the display. Generally, when average surface roughness height is large enough to create substantial anti-glare effects, then the average lateral size of the roughness features is necessarily relatively large to produce narrow-angle scattering in transmission and also wash out the images reflected by surfaces below. Such features will also produce a significant level of “sparkle” (cross-talk between adjacent image pixels). On the other hand, if the average lateral size of the roughness features is sufficiently small to minimize sparkle, the resulting scattering will be over a wider range of angles, generating “haze,” which reduces the contrast ratio of the display under ambient lighting.